I would say at least a 1/4". You can see mine here as it looks to be an inch. Its been on the car so long I forgot what size it was. And it made a ton of difference to help stop the fuel from boiling in the carb bowls. Ron

We tested this stuff years ago. Found hardwood actually worked better than phenolic spacers did. We settled on 1/2" spacers. But this was years ago for sure. Also those heat shields have been around for years, in a pump gas street car with a tight engine compartment they wore worth something I would imagine. Will definitely help with boiling fuel in the bowls for sure.

_________________________"I am not ashamed to confess I am ignorant of what I do not know."

I don't know what the minimum thickness is but I made up a 2 "one out of 1/2 " Baltic birch 9 ply plywood for the race car. Carb was no hotter than the fender, the manifold-engine was to hot to touch. I was still able to close the hood with tall intake and that spacer and air cleaner (383). Wood is one of the best insulators also.

If you really wanted to isolate the carb from the manifold you would also need to use nylon or fiber washers under the carb nuts. Probably minimal gains but thats one less spot to transfer heat.

When I had a carb my vapor lock problems were rare even with a stock hood, but it seemed to be underhood temp as opposed to engine temp that got them. I have an old trans temp gauge hanging near the master cylinder. When it reads over 180* is when vapor lock problems seem to start. In a stock engine compartment full of hot air I am not sure you can make much of a difference. I never had room for a spacer so I was never able to try.

The best way to keep a carb running nice and cool is a bypass fuel regulator after the carb so cool fuel is always available. Even with this setup, the secondary fuel bowl can get really hot on those 100 mile drives between fill ups

The best way to keep a carb running nice and cool is a bypass fuel regulator after the carb so cool fuel is always available. Even with this setup, the secondary fuel bowl can get really hot on those 100 mile drives between fill ups

Thats true. I have got away with my deadhead setup but I have a return type regulator I would like to install. Course I have a stock tank and will have to find a sending unit with a port or take mine out and make a port for a return line. I have also heard wood is the best isolator to use and I may switch to wood soon. Ron